Hops, in the form of either the ground dried plant or an extract, are used in brewing to give the malt beverages, such as beer or ale, their characteristic bitter flavor and pleasant aroma. The hops or a hop extract may be added to boiling wort in the brewing kettle. An isomerized hop extract, if it is highly purified, may be added post kettle, i.e. after the wort has been boiled or after fermentation.
The primary hop constituents used in the brewing process are the alpha acids, the beta acids, the uncharacterized soft resins and the hop oils. The alpha acids are known as humulones and the beta acids are known as lupulones. The alpha acids are the precursors of the bitter substances in beer. The beta acids or lupulones have low solubility in kettle wort and beer and play a relatively minor role in the brewing process.
During brewing, chemical changes are made in the humulones resulting in the formation of compounds known as isohumulones, i.e., isohumulone, isocohumulone and isoadhumulone. These iso-alpha acids are formed in the kettle during the boiling stage of the normal brewing process and are the primary contributors to the characteristic bitter flavor of beer and ale.
Hop extracts have been used in brewing beer for a number of years. The reasons are several fold. When whole hops are added to the kettle, the yield of isohumulone is poor, e.g. 20-25% based on the humulone present in the hops. However, the conversion of humulones in a hop extract to isohumulones can be very high, e.g. 80%. Furthermore, the utilization of the pure isohumulones in a preisomerized extract which is added post kettle is known to be extremely high, e.g. 70-90%.
In order to use a hop extract post kettle, it must contain isohumulones of a high degree of purity and only insignificant amounts of the other components of a preisomerized extract such as lupulones, waxes and other hop insoluble residues which can cause substantial haze, i.e., turbidity or gushing, i.e., rapid carbon dioxide release.
Extracts containing isohumulones of only 80% purity, for example, cannot be added post kettle in amounts exceeding approximately 10-15 p.p.m. of isohumulone without the possibility of causing turbidity in the finished product. On the other hand, extracts containing isohumulone of high purity, 90%+, can be added post kettle at levels exceeding 20 p.p.m. without a significant increase in turbidity.
It is known that isohumulone derived from hops or an unreduced hop extract can cause light instability in malt beverages. The exposure of such a beer or ale to light can result in the beverage becoming "light struck" and having a skunky odor.
In U.S. Pat. No. 3,044,879, a method is described for preparing a hop extract which when added to beer or ale produces a light stable or "anactinic" malt beverage. The hop extract of the patent is obtained by extracting the flavor active alpha acids or humulones from the hop plant with a low boiling petroleum ether. The thus obtained humulones are then purified by treatment with methanol followed by precipitation as a lead complex, removal of the lead and re-extraction of the humulones from petroleum ether. The humulones in the extract are isomerized and reduced to finally obtain the desired hop extract.
In U.S. Pat. No. 3,798,332 a method is described in which a hop extract, which has been preisomerized and prereduced, dissolved in a water-immiscible organic solvent, e.g. hexane, is treated with aqueous KOH to give an aqueous phase containing 80%+ of the isohumulate present as potassium isohumulate of 90%+ purity. The thus obtained extract can be added to malt beverages post kettle without causing significant amounts of the haze or gushing. The organic phase which is separated from the aqueous phase in the patented process contains the remainder of the isohumulone and other hop constituents. It can be stripped of the organic solvent and added to the brewing kettle as a flavoring agent. Beverages made using either of the hop extracts obtained by the method of U.S. Pat. No. 3,789,332 are light stable or anactinic.
The present invention relates to hop extracts which may be used to prepare anactinic malt beverages and differs from the prior art primarily in that the methods of preparing such extracts is accomplished without using organic solvents.